Help me find my misfire before hillclimb in less than 2 weeks

Maybe someone here has an off the wall idea of what could be causing it. All suggestions (not pertaining to a fire) welcomed.

02 WRX stock block, ECUTEK Level 2 Tuning, Walbro Fuel Pump, Modified Stock Fuel Injectors, Tumble Valve Delete Option (dividers, shafts, and butterflies), Catless Up-pipe,34mm Turbo Inlet Restrictor,VF28 turbo , Stromung Divorced Wastegate Catless Down-pipe, Davesport Metal Catalitic Converter, Custom 3” Exhaust System.

This configuration ran fine for several years and there've been no recent changes except for battery moved to rear passenger compartment. Pulls fine to about 5,000 RPM then begins to misfire and lose power.

Things that have been tried. Moved battery back to original location. New MAF. New plugs (same problem with “old” plugs that were not very old). Swapped coil packs with a friend whose car runs fine. Fuel pressure good at 70 psi at feed to fuel rails. Knock sensor replaced. Throws no CEL codes. Compression good. Leakdown good. Older gas pumped out and fresh gas. Boost is good at ~18 lbs. Took it to Subaru dealer and had them put on the Subaru scan tool. Only things discovered was negative fuel pressure in gas tank (fixed that, bad connection on recirculating hose), and ECU sees only 12.5 volts maximum even though voltage at battery when running is 14 volts. Swapped out the alternator just in case and it made no difference. Sometimes it runs a little better than other times but always misses above 5,000. Main problem is the misfire, which causes the loss of power. And yes, I know with the restrictor I'm not really making power much above 5,000. But sometimes it's happening at 4,800 or so and I need to pull higher than 5,000 at certain points for other reasons (avoiding shifting, and shifting again, etc).

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Don Kennedy

Sounds like a crank sensor. Does it only do it under load?

Yes, I believe only under load. Although I don't often rev it that high under non load.

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Don Kennedy

Any changes to wiring harness or new sensors or gauges added recently?

Had similar issues on my Evo and don't know for sure what the cause is. We had wired up some new sensors to datalog turbo speed and also re-hooked up the throttle kicker for antilag. The misfire developed the following day. Looking like the toonerz want me to scrap the OEM wiring harness and start fresh. Also have requested I pull my injectors and get them cleaned, and thinking it also might be a good idea to send the ECU back to the manufacturer to get the circuit board checked out.

Good luck - wiring/electrical stuff sucks!

Dave

When you get a chance, wind it up and see what happens. It'll at least narrow it down to other stuff.

Had a few Dirtfish school STI's do just that, it was air filter related. They would get dirty, and cause turbulence at the maf, if they got dirty with silt, the restriction was enough to collapse the inlet hose to the turbo and they would surge really bad. What airfilter are you using? Is it spotlessly clean?

What's your plug gap?

No real changes to wiring or sensors or gauges. Wide band O2 re-installed about when this happened. Air filter is K&N and cleaned and oiled recently. Spark plugs installed by my son and I don't think he checked the gap. I'm going to check the gap on the ones that were pulled and the ones in there now.

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Don Kennedy

Where are the missing 2 volts ? If running voltage is >14.5 as it should be then PCM should be 14.5 as well as the coils and injectors..at least on a normal car.

Basic question just for clarificarion re restrictor.

You've had the restrictor on previously, yes?
It ran right with restrictor previously?

And what about what Gene said?
I had an Xratty--still do but it is now more ratty the before---and had an intermittant crap charging deal going and when it would be putting out 12.0v the thing would run majorly shitty, like crazy lean--popped a headgasket once when the battery was getting all drained down. Similar symtoms above 4500: lack of yank, sluggish...Felt like way retarded timing, manifold and turbine housing glowing dull orange..
Put it on charger and all better..

What voltage IS the ECU 'spossed to be getting?

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

I do recall walbros pull a lot of current. Especially when they start to shit the bed. Kind of an out there thing, but your pump may be taking a dump causing voltage to drop under load
Have seen weirder things with those pumps....

Restrictor has been on forever (well at least since Spitzer days) and it ran fine. Wish I knew where the missing voltage is. Guess I'm going to have to start to pull the dash out. This is the second shell we've moved the wiring harness to and my son seems to think that's the root of the problem (harness was put in this shell back in 2009). I don't necessarly agree but I've got to look into it at this point. I'll need to verify with my Subaru dealer mechanic what he thinks the ECU is supposed to be getting but he seemed to indicate that 12.5 for a max at any/all RPMs was not good. I've got a stock fuel pump I could try and see what happens. But all of this takes time and work (and wife and children and grandchildren) keeps getting in the way.

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Don Kennedy

Did the oil for the airfilter get the maf all dirty? Have you reset the ecu after each of these solutions? We did a build on an 04 sti and it was doing the same thing you're describing misfire above 5k but it was throwing a cylinder misfire cel, it was the crank sensor wasn't all the way plugged in, maybe yours is just bad...

Quote
imnotcrazy
. I'll need to verify with my Subaru dealer mechanic what he thinks the ECU is supposed to be getting but he seemed to indicate that 12.5 for a max at any/all RPMs was not good.

Verify what the Service manual says...Mechanics are humans---I think---well sorta----and they can remember stuff wrong,, Print is print---print can't change its mind or forget

As Comrade Derzhinskij used to say:


(Doveryay, no proveryay..)

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.



Edited 2 time(s). Last edit at 08/07/2013 10:38AM by john vanlandingham.

Power out of the ECU is choked for stuff that uses 5 volts but power to the ECU should be battery voltage . So 12.6 ish resting and 14.5 to 14.8 ish running. Going by your numbers as it appears there is a 2 volt drop somewhere, that is a large drop. Green wire, partially shorted wires , bad ignition switch, one helluva draw (something would be pretty damned warm. A typical ballast resistor in the old days dropped a couple volts and would burn a hand pretty fast.

Quick thing would be jump a good battery source , 14.5, straight to the ECU power. See if it is still 14.5. This may not be your miss but that voltage is wacky and electronic modern cars like voltage. I somewhat remember the old racing days that a car running on battery voltage would rev about 2k lower than one running an alternator.

Twice the crank sensor has been mentioned. I'll swap it out tonight. A problem I've had for some time is with the ignition switch. Something funky inside that depending on the position of the key, causes the door open light to come on and a small draw on the battery. I started swapping it out last night and need to finish that tonight.

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Don Kennedy